这段代码非常有用，如果你下载了一个文件，网站提供了hash结果，你可以对你下载下来的文件进行hash运算，以验证下载的文件是否正确。
<html>
<head>
    <title>Hash (Check) Files</title>
    <style type='text/css'>
        #ok{color:green;}
        #nono{color:red;}
    </style>
</head>
<body>
<?php
if(!empty($_FILES)){
    if ($_FILES["file"]["error"] > 0){
        switch($_FILES["file"]["error"]){
            case 1:
                echo "<b id='nono'>Error: The uploaded file exceeds the upload_max_filesize directive in php.ini</b><br>";
                break;
            case 2:
                echo "<b id='nono'>Error: The uploaded file exceeds the MAX_FILE_SIZE directive that was specified in the HTML form.</b><br>";
                break;
            case 3:
                echo "<b id='nono'>Error: The uploaded file was only partially uploaded.</b><br>";
                break;
            case 4:
                echo "<b id='nono'>Error: No file was uploaded.</b><br>";
                break;
            case 6:
                echo "<b id='nono'>Error: Missing a temporary folder.</b><br>";
                break;
            case 7:
                echo "<b id='nono'>Error: Failed to write file to disk.</b><br>";
                break;
            case 8:
                echo "<b id='nono'>Error: A PHP extension stopped the file upload.</b><br>";
                break;
            default:
                echo "<b id='nono'>Unknown error occured.</b><br>";
        }
    } else {
        echo 'Upload: ' . $_FILES['file']['name'] . '<br>';
        echo 'Type: ' . $_FILES['file']['type'] . '<br>';
        echo 'Size: ' . (round($_FILES['file']['size'] / 1024, 2)) . ' Kb<br><br>';
        if(array_search($_POST['algo'], hash_algos())===false){
            echo 'Unknown hashing algorithm requested.<br>';
        } else {
            echo 'Hashing Algorithm: '. $_POST['algo'] . '<br>';
            $hash = hash_file($_POST['algo'], $_FILES['file']['tmp_name']);
            echo 'Calculated hash: ' . $hash . '<br>';
            if($_POST['exphash']!=='none' && !empty($_POST['exphash'])){
                echo 'Expected hash: &nbsp;&nbsp;' . $_POST['exphash'] . '<br><br>';
                echo ($hash==$_POST['exphash'])? '<b id="ok">Hash matched expected value.</b>' : '<b id="nono">Hash did not match expected value.</b>';
                echo '<br>';
            }
        }
    }
    ?>
    <br>
    <button onClick="document.location.reload(true)">Again</button>
    <?php
} else {
    ?>
    <form action="" method="post" enctype="multipart/form-data">
        <input type="hidden" name="exphash" value="none">
        <label for="file">Filename:</label>
        <input type="file" name="file" id="file">
        <input type="submit" name="submit" value="Submit" /><br>
        <label>Expected hash(optional): <input type="text" name="exphash" size="100"></label>
        <br><br>Choose an algorithm (This is the list of all the available algorithms in your php installation)<br>
        <?php
        foreach(hash_algos() as $algo){
            if($algo=='md5'){
                echo "<label><input type='radio' name='algo' value='$algo' checked='checked'>$algo</label><br>";
            } else {
                echo "<label><input type='radio' name='algo' value='$algo'>$algo</label><br>";
            }
        }
        ?>
    </form>
    <?php
}
?>
</body>
</html>
<?php

/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2019/8/21
 * Time: 19:48
 */
class 文件进行hash运算
{

}